Binary uses only zero and one, and it is the counting system at the heart of modern computers.

The longer version

Counting in base two means each column doubles instead of increasing tenfold, so the places read ones, twos, fours, eights, and onward. The number thirteen becomes one eight, one four, no two, and one, written as a string of four marks. No digit larger than one is ever needed.

Machines favour it because a switch has two dependable conditions, conducting or not, and building circuits that must distinguish ten voltage levels is far less reliable. Arithmetic then collapses into a handful of logical rules on bit pairs. Long strings are hard for people to read, which is why programmers group them and switch to base sixteen.

Where this entry sits

This section collects odd corners of mathematics, from stubborn prime numbers to counting systems older than modern schools. Expect famous constants, probability puzzles, shapes that break everyday intuition, and numbers far too large to picture. The full list sits on the Numbers and Math page, where every entry is listed in order.